However, the obvious solution is to use a html browser because of the hypertext capabilities. Writing my own was pointless as there are already numerous useful implementations. The one I've chosen is Chimera, which is written by John Kilburg. Chimera uses the Athena widget set; for this version I have used the Athena 3D widgets, giving it a more modern look.
There is nothing magic about the Chimera program, any html browser will do. The environment variable SIAGHELP can be set to the name of another browser, thus overriding the default.